Textbook of Veterinary Nuclear Medicine

2007 Radiology Exam - Artifacts Case 1

2007 Technical Errors and Artifacts Case 1

Objective of the Case
1. Identify the artifact or problem
2. Describe how the artifact/problem may have occurred
3. Discuss how to avoid the artifact/problem or if inevitable, how this would affect interpretation of the study
4. Discuss how this particular artifact would affect interpretation of the study.

Information provided to Candidate
1. Written instructions above.
2. The candidate was directed to the flame shaped alternating low and high signal intensity artifact distorting the MR image in the region of the pharynx and skin ventral to this area, and asked to address the above written questions regarding this artifact.

See image below. Click to enlarge.

Findings Expected from Candidate
1. Identify artifact: Magnetic susceptibility artifact.
2. The artifact is caused by a ferromagnetic object in or near the patient’s pharyngeal region. The ferromagnetic material causes a disruption of the local magnetic field and results in distortion of regional anatomy and alteration in tissue signal.
3. The candidate was expected to advise evaluation of the patient and surrounding area for metal materials by direct inspection and with radiographs of the pet if direct inspection revealed no metallic material.
4. The candidate should relay that the artifact obscures and distorts regional anatomy limiting evaluation of the area involved.

Summary of Overall Candidate Performance
The question was worth a total of 6 points. The average score was 3.67/6.0 or 56%. Many candidates believed the artifact to be related to motion, suggesting swallowing. Candidates that recognized the object as a magnetic susceptibility artifact did well in explaining the cause and preventive measures necessary to address the artifact.

Follow up
In this case this artifact was caused by a small spring within the valve at the end of the endotracheal tube designed to prevent cuff deflation. Repositioning of the endotracheal tube was performed after the artifact was observed and the study was continued with the artifact no longer interfering with image quality.